This invention relates to packaging films having special surface characteristics which eliminate air entrapment between the film and packaged articles having smooth surfaces.
Skin packaging is a special form of packaging that uses the product being packaged as a mold over which a heated plastic film is drawn by vacuum and then heat sealed to a backing. A frequent problem associated with this and similar types of packaging is the entrapment of pockets of unevacuated air between the film and the surface of the product. The entrapped air pockets create the illusion that there is water on the surface of the product; this "wet look" is especially severe when skin packaging a glossy surfaced item with a glossy film because together the two surfaces allow for entrapment of air pockets. The "wet look" detracts from the appearance and marketability of skin packaged products.
U.S. Pat. No. 3,595,827 discloses films of ethylene interpolymers, such as ethylene/acrylic acid ionomers. The slip and antiblocking properties of the films are improved by addition of 0.02 to 1.0% of an N-substituted fatty acid amide and about 0.01 to 2.0% of synthetic amorphous silica having an average particle size of about 0.5 to 8.0 microns. Comparative examples in which the synthetic amorphous silica is used alone exhibit at best an insignificant effect on the slip properties.
U.S. Pat. No. 3,474,063 discloses films of carbon chain-saturated polymers such as ionomers and additives such as N,N'-dialiphatic thiodipropionamides for improving the slip and block properties of such films. In addition, from 500 to 5000 p.p.m. of finely divided silica can be used to accelerate the effectiveness of the additive in highly glossy films. The silica may have, for examples, an average particle size of 4 microns.
U.S. Defensive Publication T877,077 discloses an ionic copolymer film having improved gloss and slip properties by addition of an oleamide and about 0.1% to about 0.5% of a siliceous material having an average particle size of about 0.1 to about 10 microns. The film is useful for packaging uses.
U.S. Pat. No. 4,389,450 discloses a multiple layer packaging film, one layer of which is a sealant. The sealant layer is e.g. a blend of EVA copolymer and ionomer, and contains a slip additive to control tackiness. A composition of 4% erucamide, 4% stearamide and 20% silica antiblock in an ethylene vinyl acetate base resin is disclosed as a prior art slip agent.